GOP lawmakers avoiding meetings with constituents because they are worried about boisterous crowds that have shown up at recent town hall gatherings "have not seen anything yet," Sen. Bernie Sanders warned Thursday.

In an interview on CNN's "Erin Burnett OutFront," the Vermont Independent said if lawmakers "don't have the guts to face your constituents, you shouldn't be in the United States Congress."

"If you need police at the meetings, that's fine, have police at the meetings, have security at the meetings," he said.

"But don't use that as an excuse to run away from your constituents after you support repealing the Affordable Care Act, doing away with pre-existing conditions, if you're going to do all those things, answer the questions your constituents have."

Sanders warned those GOP lawmakers will "see more" protests.

"I think the Republicans have not seen anything yet," he said. "They're worried about the protests, they'll see more."

"This coming Saturday we believe there will be well over 100 protests, most of them in Republican offices around the country, district offices, demanding that Republican members of Congress meet with their constituents and answer the questions that their constituents have," he added.

Sanders also pushed back at Sen. Ted Cruz's description of Democrats as "bat crap crazy," charging the Texas Republican and "many of his colleagues . . . are living in an alternative universe."

"I don't think they know what's happening to working families, to the elderly people," he said, adding the loss of Obamacare also will put young people and those with pre-existing conditions in peril.

"Maybe Sen. Cruz should start answering those questions, talking to his constituents about those issues rather than making fun or disparaging others," he said.

Sanders said protests that have erupted since President Donald Trump took office are not phony rage.

"What's going on now is people all over this country are beginning to rise up," he said.

"They're demanding answers to what happens. . . . I think you are seeing people organizing effectively, but unlike the Tea Party, this is not being funded by the billionaire class. . . . It's not just Democrats. There are Republicans. . . ."

GOP lawmakers avoiding meetings with constituents because they are worried about boisterous crowds that have shown up at recent town hall gatherings "have not seen anything yet," Sen. Bernie Sanders warned Thursday.